Unprotected wood structures are susceptible to degradation by fungi and insects such as termites, which can cause substantial damage to wood building structures. Property damage in US alone is estimated to be in the neighborhood of 1 billion dollars a year. Various processes and chemicals have been used to treat wood to protect it from insect degradation. For example, preservatives, such as Copper Chrome Arsenate (CCA), ACC, ACQ and borate, have been impregnated in wood by a variety of processes. One popular method of integrating chemicals in the wood is by a vacuum/pressure treatment in the presence of an aqueous solution containing the preservative.
While the known methods are relatively successful at introducing preservatives in wood products, they necessitate the used of costly systems and may not be energy efficient. Accordingly improved methods are desirable. Also the resulting product is very prone to wash out by exposure to water. In particular, borate-treated lumber is particularly prone to leaching or wash-out by rain water and cannot be used in exterior structures. Methods have been developed that attempt to prevent the leaching out of preservatives. One such method is described in U.S. Pat. No. 6,426,118 to Barnisin. The method consists in drying the wood before infusing the preservative followed by further drying and the infusion of a waxy solid that constitutes a barrier to water and prevent leaching of the active ingredient. This method suffers from the need to treat the wood with not only the active ingredient but also the waxy solid which makes the treatment longer and more costly. Furthermore the wax may adversely affect further treatment of the wood with coatings such as paint.
There is thus a need for an improved process for treating wood whereby the impregnated water-soluble preservatives are inhibited from leaching out of the wood.